Device for determining the actual vehicle speed

ABSTRACT

An apparatus for determining inherent vehicle velocity determines the inherent vehicle velocity using the pre-crash sensor suite. The determination is performed on the basis of signals reflected from road surfaces. The determination is performed only when a predefined operating state exists, such as a locked, slipping or suspended wheel.

BACKGROUND INFORMATION

It is known from German Patent Application No. DE 39 09 644 to perform ameasurement of the inherent velocity of a vehicle in accordance with theDoppler radar principle, a signal reflected from the ground beingutilized.

SUMMARY OF THE INVENTION

The apparatus according to the present invention for determininginherent vehicle velocity has the advantage that the evaluation ofinherent vehicle velocity by means of a pre-crash sensor suite on thebasis of signals reflected from the ground is used only when apredefined operating state exists. This predefined operating state maybe, for example, locked wheels, slipping wheels, or wheels suspended inthe air. The reason is that these operating states mean that ameasurement of the inherent velocity by way of wheel rotation speedfails. The inherent velocity measurement is therefore then performedusing the pre-crash sensor suite on the basis of signals reflected fromthe ground.

It is particularly advantageous that the pre-crash sensor suite has aradar sensor suite. It is furthermore advantageous that the apparatuscompares the signal reflected from an object with the inherent vehiclevelocity in such a way as to classify the object. Specifically, if theobject possesses, on the basis of the reflected signals, a relativemotion with respect to the vehicle that is equal to the inherentvelocity, it is then a stationary object. That stationary object couldthen also be used to determine the inherent velocity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a manner of operation of the apparatus according to thepresent invention.

FIG. 2 is a block diagram of the apparatus according to the presentinvention.

FIG. 3 is a first flow chart.

FIG. 4 is a second flow chart.

DETAILED DESCRIPTION

In an airbag algorithm at present, signals from impact sensors such asacceleration sensors are evaluated. The relative velocity between thevehicle and a crash object, as well as the inherent velocity, areimportant parameters for obtaining a better determination of thetriggering time. These parameters can be ascertained by means of apre-crash sensor suite. Usually, however, the inherent velocity isdetermined in the ESP/ABS control unit by means of wheel rotationspeeds. This information is no longer correct, however, in certainoperating states such as locked or spinning or suspended wheels.

The inherent velocity is an important variable for ESP/ABS function. Anexact estimate in critical situations, e.g. locked wheels, thus alsoimproves vehicle stability.

It is consequently provided according to the present invention todetermine the inherent vehicle velocity in such operating states bymeans of the pre-crash sensor suite. This is accomplished on the basisof signals reflected from the ground, i.e. from the road surface.Because the distance and angle of the radar beams with respect to theroad surface is constant, the signal time from transmission to receptionis an indication of the inherent velocity of the vehicle.

Because of the wide opening angle of the pre-crash sensor, in additionto the actual usable signals from oncoming or stationary obstacles,signal components deriving from the road are also obtained. From theseconstantly present signal components, the inherent velocity of thevehicle can then be calculated. The pre-crash sensor suite canadvantageously use a radar sensor suite here, but it is also possible touse an ultrasonic sensor suite or lidar technology, or other signalsthat are emitted and reflected back.

FIG. 1 shows the manner of operation of the apparatus according to thepresent invention. A vehicle 10 has a pre-crash sensor suite 11, here aradar sensor suite, which here emits, for example, radar beams 13 and15. Radar beam 13 is reflected from road surface 12, while radar beam 15is reflected from object 14. Because the angle of radar beam 13 withrespect to the road is always the same, the signal transit time fromradar sensor 11 to road 12 is always the same. The signal transit timethus provides an indication of the inherent vehicle velocity. The signaltransit time with respect to obstacle 14 drops with decreasing distance.The signal sequence of the reflected signals is, however, likewise anindication of the inherent vehicle velocity if obstacle 14 is notmoving. A classification of obstacle 14 is thus possible.

FIG. 2 is a block diagram of the apparatus according to the presentinvention. A pre-crash sensor suite 20 is connected to a signalprocessing system 21. Signal processing system 21 amplifies, filters,and digitizes the signals of pre-crash sensor suite 20. The digitalsignals are then transferred from signal processing system 21 to acontrol unit 22. This control unit 22 is in this case, by way ofexample, the control unit for the restraint means. A wheel rotationspeed sensor suite 23 also, however, transfers to control unit 22 asignal that represents the inherent vehicle velocity. If it is thendetected by means of the vehicle dynamics control system that a wheel isslipping or locked or suspended, airbag control unit 22 then uses thesignals of pre-crash sensor suite 20 to determine the inherent vehiclevelocity. The inherent vehicle velocity is an important parameter fordetermining the severity of a crash. As a function thereof, control unit22 then activates restraint means 24. Restraint means 24 includeairbags, belt tensioners, or roll bars.

FIG. 3 explains the manner of operation of the apparatus according tothe present invention in a first flow chart. The method begins at methodstep 300. Method step 301 checks, specifically on the basis of data froma vehicle dynamics control system or an ABS control unit, whether acondition exists that necessitates determination of the inherentvelocity by means of the pre-crash sensor suite. These conditionsinclude those that make it impossible to determine the inherent velocityon the basis of wheel rotation speed. These are locked, slipping, orsuspended wheels. If such is not the case, then in method step 303 theinherent velocity is determined on the basis of wheel rotation speed. Ifit is the case, however, then in method step 302 the inherent velocityis determined as presented above on the basis of the pre-crash sensorsuite, based on the signal reflected from the road surface.

FIG. 4 explains the manner of operation of the apparatus according tothe present invention in a second flow chart. The method begins atmethod step 400. In method step 401, an evaluation is performed ofsignals reflected from an object. The evaluation is made in such a waythat the velocity of the object sequence is evaluated. The reason isthat the inherent velocity of the vehicle can therefore be determined ifthe object is stationary. Method step 402 consequently evaluates whetherthe velocity that can be determined on the basis of the object sequencecorresponds to the inherent velocity. If such is the case, method step403 then establishes that the object is stationary. If it is not thecase, method step 404 then establishes that the object is moving.

When the beam component reflected back from the road is evaluated, whatis obtained is an object that is always at the same distance in front ofthe vehicle. It is made up of a sequence of objects that are movingtoward the vehicle. When the velocity of the object sequence is thenevaluated, it is then found to correspond to the inherent velocity.Because of the fixed distance of the object and the object velocity thatis directed toward the vehicle, the object can be distinguished fromcrash-relevant objects and thus employed for determination of theinherent velocity.

1-4. (canceled)
 5. An apparatus for determining inherent vehiclevelocity, comprising: a pre-crash sensor suite for determining theinherent vehicle velocity, the pre-crash sensor suite being configuredin such a way that when a predefined operating state exists, thepre-crash sensor suite determines the inherent vehicle velocity as afunction of a signal reflected from the ground.
 6. The apparatusaccording to claim 5, wherein the pre-crash sensor suite has a radarsensor suite.
 7. The apparatus according to claim 5, wherein theoperating state is a locked wheel.
 8. The apparatus according to claim5, wherein the operating state is a spinning wheel.
 9. The apparatusaccording to claim 5, wherein the operating state is a suspended wheel.10. The apparatus according to claim 5, further comprising anarrangement for comparing signals reflected from an object with theinherent vehicle velocity in such a way that the object is classified.